Patients with coronavirus disease 2019 (Covid-19) have a profound hypercoagulable state, and complicating venous thrombotic events are common.1-3 Abnormalities in coagulation screening measures, including a prolonged activated partial-thromboplastin time (aPTT), have been reported in patients with Covid-19.4 This finding could be seen as a reason to avoid the use of anticoagulation at both therapeutic and prophylactic doses.
A prolonged aPTT may indicate a clotting-factor deficiency or the presence of an inhibitor of coagulation that is either specific (e.g., antibody to factor VIII) or nonspecific (e.g., lupus anticoagulant). Lupus anticoagulant can affect in vitro tests of blood coagulation but typically is not associated with bleeding. As part of the antiphospholipid syndrome, lupus anticoagulant is associated with a thrombotic risk. We investigated the cause of prolonged aPTT in patients with Covid-19.